In a mobile communication network, a user A may use a terminal to register a call forwarding number, such as Call Forwarding Unconditional (CFU) or Call Forwarding Conditional (for example, call forwarding on busy, call forwarding on mobile subscriber not reachable and call forwarding on no reply), so that a call to the user A may be forwarded to a number C. That is, when another user dials a number of the user A, if a condition is met, the call is connected to a call forwarding party C and the call may be answered by the call forwarding party C. Some important incoming calls may be prevented from being missed under some conditions where the user A cannot answer the phone.
However, a mobile user, such as a user B, may use a terminal to input a number of any other user as a forwarding number of the user B without asking the other user for an agreement or permission when registering the forwarding number through the terminal, so that a malicious harassment may be caused.